Looking for current and maintained information and documentation on (Linux ) Open Source High Availability HA Clustering?You probably should be reading the Pacemaker site clusterlabs.orgThis site conserves Heartbeat specific stuff. See Site news for details.

DRBD

From Linux-HA

Linbit's system for mirroring blockdevices (filesystems, VM images, whatever) across the Network,
typically a dedicated LAN, but also cabable of WAN replication,
written by Philipp Reisner
and Lars Ellenberg

This is the general replication technology which is most commonly used by
members of the Linux-HA community. By the way, DRBD is a registered trademark
of Linbit.

The DRBD User's Guide is excellent documentation
and reference, you are strongly encouraged to thoroughly read it.
Learn how to set it up manually and how things work. Use DRBD manually to get a
feeling for what it does. Then you may start thinking about using it as a
cluster resource.